Biology Chapter 2 Movement of Substances

Question 1

Definition of diffusion

Answer 1

The net movement of particles from a region where they are of higher concentration to a region where they are of lower concentration, that is, down a concentration gradient
P.S. It’s a gradual thing, does not need energy to occur

Question 2

How is a concentration gradient related to diffusion?

Answer 2

• The movement of fluid particles is random
• Particles will diffuse down their concentration gradient
• The steeper the concentration gradient for a substance, the faster the rate of diffusion for that substance

Question 3

What is net movement?

Answer 3

• All particles move in a constant random motion
• At all time, particles are moving in both directions
• However, if a concentration gradient exists, more particles will move in the direction down the concentration gradient
• Net movement has occured

Question 4

Factors that affect the rate of diffusion

Answer 4

Concentration gradient
- Steeper concentration gradient = faster rate of diffusion
Diffusion distance - thickness
- Shorter diffusion distance = faster rate of diffusion
Surface area to volume ratio
- Greater surface area to volume ratio = faster rate of diffusion

Question 5

What can and cannot diffuse out of a partially permeable membrane

Answer 5

Can- ink, iodine, glucose, salt, water
Cannot- starch, sucrose, fats and protein

Question 6

How can the size of molecules affect diffusion through a partially permeable membrane?

Answer 6

If the size of the molecules are too, big they cannot pass through there ppm. For example, sucrose, starch, proteins and fats

Question 7

Characteristics of diffusion

Answer 7

• Process is passive
• Can occur both in the presence and absence of a partially permeable membrane
• Involves any molecules
• occurs down a concentration gradient

Question 8

Definition of osmosis

Answer 8

The net movement of water molecules from a region of higher water potent ion to a region of lower water potential , that is down a water potential gradient, through a partially permeable membrane

Question 9

What is water potential?

Answer 9

A measure of the tendency of water molecules to move from one place to another

Question 10

How is water potential related to osmosis?

Answer 10

• A dilute solution (lower solute concentration) has a higher water potential
• A concentrated solution (higher solute concentration) has a lower water potential
  (Solute concentration is the amount of salt/sugar dissolved in the solution. Water potential is inversely proportional to solute concentration)

Question 11

Characteristics of osmosis

Answer 11

• process is passive
• can occur only in the presence of a partially permeable membrane
• involves ONLY water molecules
• occurs down a water potential gradient

Question 12

Similarities between diffusion and osmosis

Answer 12

• Both involves net movement of molecules down a concentration gradient
• Both are passive process as they do not need energy to occur

Question 13

Differences between diffusion and osmosis

Answer 13

• Diffusion involves any small molecules, but osmosis only involves water molecules
• Diffusion can occur in the presence or absence of a partially permeable membrane, but osmosis can only occur in the presence of a partially permeable membrane

Question 14

How does osmosis affect living organisms?

Answer 14

Cells are living osmotic systems

Question 15

Effects of osmosis on animal cells
What happens to an animal cell (e.g. red blood cell) when it is placed in a solution with higher water potential (e.g. distilled water)

Answer 15

1. The solution has a higher water potential as compared to the red blood cell’s cytoplasm
2. There will be a net movement of water molecules from the solution to the red blood cell’s cytoplasm
3. Down a water potential gradient, through a partially permeable cell membrane, by osmosis
4. The red blood cell expands and burst
   If asked to explain why- animal cells are fragile, with only the cell membrane holding the cell together. Animal cells do not have a cell wall to support the structure, thus bursting if there is too much water

Question 16

What happens to an animal cell when it is placed in a solution with LOWER water potential (e.g. concentrated sucrose solution)

Answer 16

1. The concentrated sucrose solution has a lower water potential as compared to the red blood cell’s cytoplasm
2. There will be a net movement of water molecules from the red blood cell’s cytoplasm to the concentrated sucrose solution
3. Down a water potential gradient, through a partially permeable cell membrane, by osmosis
4. The red blood cell will become crenated

Physical appearance of the cell:
- Shrink in size
- have tiny spikes on its cell’s surface membrane

Question 17

What happens to an animal cell when it is placed in a solution with the same water potential

Answer 17

1. The solution has the same water potential as to the animal cell’s cytoplasm
2. There will be no net movement of water molecules from the red blood cell’s cytoplasm to the solution, and vice versa
3. No osmosis will take place
4. The red blood cell will remain the same in size, shape and mass

Question 18

Effects of osmosis on plant cells
What happens to a plan cell when it is placed in a solution with HIGHER water potential

Answer 18

1. The solution has a higher water potential as compared to the plant cell’s cell sap
2. There will be a net of water molecules from the solution to the plant cell’s cell sap
3. Down a water potential gradient, through the partially permeable membrane, by osmosis
4. The plant cell becomes more turgid and firm. It’s vacuole increases in size as well
   ( This is good for plants as they do not have a skeleton, so a lot of water is good for the cell to be turgid and firm, allowing the plant to be upright )

Question 19

What happens to a plant cell when it is placed in a solution with lower water potential ( e.g. concentrated sucrose solution )

Answer 19

1. The solution has a lower water potential as compared to the plant cell’s cell sap
2. There will be a net movement of water molecules from the plant cell’s cell sap to the solution
3. Down a water potential gradient, through the partially permeable membrane, by osmosis
4. Plant cell becomes flaccid and plasmolysed

Physical appearance of cell:
- Cell membrane and cytoplasm shrink away from the cell wall
- The size of the vacuole also decreases

Question 20

What happens to a plant cell when it is placed in a solution with the same water potential

Answer 20

1. The solution has the same water potential as compared to the plant cell’s cell sap
2. There will be no net movement of water molecules from the plant cell’s cell sap to the solution, and vice versa
3. No osmosis will take place
4. Plant cell will remain the same in size, shape and mass

Question 21

Why is maintaining turgor important in plants?

Answer 21

1. Turgor plays an important role in maintaining the shape of soft tissues in plants, for the plant’s turgidity
2. It keeps herbaceous plants firm and upright
3. Loss of turgidity will cause the plant cells to become flaccid and plasmolysed, the plant would wilt
4. Changes in turgor also cause the movements of some plant parts e.g. regulate the opening and closing of stomata. Turgor in guard cells causes stoma to open in the day, loss of turgor in guard cells causes stoma to close at night

Question 22

What is wilting?

Answer 22

When rate of evaporation of water from the leaf cells is higher than the rate of water absorption from the root hair cells, there will be net movement of water molecules out of the plant cells to the surroundings, the plant cells will then lose their turgidity, thus the plant wilts

Question 23

Why do guard cells bend?

Answer 23

Uneven expansion occurs as there is a difference in thickness of cell wall

Question 24

Surface area to volume ratio recall

Answer 24

Greater surface area to volume ratio = faster rate if diffusion or osmosis

Question 25

What does surface area to volume ratio mean to a cell?

Answer 25

As a cell becomes bigger (increasing volume, its surface area to volume ratio decreases

Question 26

How are cells adapted for the absorption of materials?

Answer 26

• Cells which function in absorption have an increased surface area to volume ratio
  For example
  1. root hair cells have a long and narrow protrusion
  2. Villi have finger-like projections
  3. Red blood cells have a circular biconcave shape

Question 27

Definition of active transport

Answer 27

The process in which energy is used to move particles of a substance across a membrane against its concentration gradient, that is, from a region where the particles of lower concentration to a region where they are of higher concentration
(net movement does not need to be mentioned for this. Also reminder diffusion and osmosis does not need energy)

Question 28

Active transport observed in plants

Answer 28

• Since active transport requires energy, active transport will only occur in respiring living cells, where there are a abundance of mitochondria to release large amounts of energy through the oxidation of glucose
• Where there is a higher concentration of dissolved mineral salts in the root hair cells’ cell sap as compared to the soil, these dissolved mineral salts will be absorbed by root hair cells via active transport

Question 29

Active transport observe in cactus

Answer 29

this is a break hehe, refer to your notability notes

Question 30

Active transport observed in humans (small intestine)

Answer 30

When there is a higher concentration of glucose and amino acids in the small intestine epithelial cells as compared to the lumen of the small intestine, these glucose and amino acids will be absorbed by the small intestine epithelial cells via active transport.
( Absorption of nutrients in small intestine can be both diffusion and active transport, but under starvation, active transport is used only)

Question 31

Characteristics of active transport

Answer 31

• Process is active
• Can occur only in the presence of a partially permeable membrane
• involves any molecules
• occurs against a concentration gradient